1. Field of the Invention
The present invention relates to a doping method, and particularly to a doping method by annealing with a high intensity light source, and a manufacturing method for a semiconductor device.
2. Description of the Related Art
It is possible to achieve improvements in a semiconductor device performance of a large scale integration (LSI) and the like by increasing integration, or to put it more plainly, by miniaturization of the elements that build up a semiconductor device. Thus, LSIs are increasingly large-scale while miniaturization of elements such as metal-oxide-semiconductor (MOS) transistors is being taken to a whole new level. Along with (MOS) transistors is being taken to a whole new level. Along with the miniaturization of elements, parasitic resistance and short channel effects on MOS transistors and the like, are increasing. Thus, there is increased importance placed on the formation of low resistance layers and shallow pn junctions.
For forming a shallow pn junction with a thickness of or below twenty nm, a thin impurity doped region is formed using ion implantation in a semiconductor substrate, with low acceleration energy. The impurities doped in the semiconductor substrate are activated by annealing, thus forming a shallow impurity diffusion region.
However, the diffusion coefficients of p-type impurity atoms such as boron (B), and n-type impurity atoms such as phosphorus (P) or arsenic (As), in the crystal of the silicon (Si) substrate, are large. In the processing time needed to perform rapid thermal annealing (RTA) using current halogen lamps, impurities diffuse to both the interior and exterior of a semiconductor substrate. As a result, it is impossible to form a shallow impurity diffusion region having a high concentration of impurities on the semiconductor substrate. Also, it becomes difficult to activate a high concentration of impurities if the temperature of the RTA process is decreased in order to control the diffusion of the impurities. Because of such difficulties it is difficult to form a shallow impurity diffusion region having low resistance and a high concentration of activated impurities.
In recent years, a flash lamp annealing method using a xenon (Xe) flash lamp and the like, which can instantly supply the energy essential to impurity activation, is being tested as a solution to the RTA problem. A Xe flash lamp has a quartz glass tube filled with Xe gas in which electrical charges stored in capacitors, and the like, are instantaneously discharged. As a result, it is possible to emit a high intensity white light within a range of several hundred μs to several hundred ms. It is possible to attain the heat energy required for impurity activation in the instantaneous heating of a semiconductor substrate absorbing flash lamp light. Therefore, it is possible to activate a high concentration of impurities while leaving the concentration profile of the impurities implanted into the semiconductor substrate virtually unchanged.
However, in a flash lamp annealing method, there is a problem of a decrease in thermal efficiency due to light of the flash lamp being reflected off of the surface of a semiconductor substrate. Because of this drop in thermal efficiency, it is impossible to sufficiently activate impurities. An irradiation energy density of 30 J/cm2 or more is needed to activate a high concentration of impurities. Semiconductor devices have various materials arranged in fine patterns that are often uneven and irregular. When high intensity white flash lamp light is irradiated onto a semiconductor substrate, there are differences in refractive indices because of the various materials included in elements of a semiconductor device. Thus, incident flash lamp light is refracted and light interfere occurs inside the semiconductor substrate. In a case in which irradiation energy density of flash lamp light is large, there is a concern that hot spots may be formed. Such hot spots arise when flash lamp light undergoes interference and concentrates in spots within a semiconductor substrate. Thermal stresses between various materials used in a semiconductor device may be generated due to differences in thermal properties such as heating efficiency, specific heat, thermal conductivity, and coefficient of thermal expansion. As a result, the thermal stress induced within a semiconductor substrate may increase. Crystal defects, such as slip and dislocation, caused by thermal stress inside a semiconductor substrate may be generated, so as to decrease the production yield rate.
In an attempt to increase an activated concentration of impurities, there is a method for increasing the solid solubility of impurities, in which a surface layer of a semiconductor substrate is amorphized by ion implantation using a group IV element, such as Si and germanium (Ge). However, crystal defects caused by ion implantation of group IV element will remain after activation annealing. Therefore, ion implantation of group IV element may be a cause for increasing leakage current of a pn junction, and off-state current of a transistor. Thus, in current flash lamp annealing methods, although it may be possible to form an impurity diffusion layer having a shallow pn junction, it is difficult to form a low resistance diffused layer having no crystal defects.